The conventional monitor usually has several knobs beside the screen for adjusting various functions of the monitor; then, the monitor can be adjusted manually in brightness, the vertical size, the horizontal size and the contrast thereof. Such adjustment is based on the adjustment of several rheostats through the tuning knobs respectively; when a rheostat is adjusted, the circuit following the rheostat will also be changed; such an adjustment circuit is shown in FIG. 1, in which the resistance between two points A and B will vary upon the knob being turned; the point B is connected with the next stage of circuit. The image of the conventional monitor is adjusted only by means of a manual adjusting method; after each adjustment, the image will stay as it is without change until a further adjustment is made; as a result, the monitor in real use has to be adjusted manually to obtain a fixed brightness and contrast. Consequently, a user after a given period of time often has tired eyes. Furthermore, some users often forget the time when working before such a monitor, i.e., forgetting to have a break which is necessary; another, a user of such a monitor is subject to suffering from a non-remedial eye disease after working for along period of time because of his (or her) eyes being under a tired and pressure condition for a long time.